Local Area Networks that use radio waves for the unguided transmission of data and protocols come to be known as wireless LANs. The term “wireless” is not completely descriptive since these networks merely reduce the quantity of wire needed to construct a LAN. Wireless LANs may more adequately be described as local area networks in which a portion of the communications are wireless. This follows the tremendous growth in wireless communication products including cellular telephones, wireless personal computers and like devices. Thus, the wireless LAN is conventionally a geographically defined facility, such as a business and manufacturing site, a university site or a government facility within which the workers can unhook from the network connections and move about without restriction to access the Wireless LANs from virtually anywhere within the facility. Car rental facilities use wireless LANs to facilitate check-ins; traders on stock exchange floors use mobile wireless LANs for entering trades; students on university campuses may access lectures, books and notes from any point; medical professionals making rounds may access medical data wirelessly from any point in the hospital plant. Some good background on wireless LANs may be found in the text, Peter Norton's Complete Guide to Networking, SAMS Division of MacMillan Computer Publishing, Indianapolis, Ind., 1999, pp. 49–62.
A wireless LAN may be as simple as two laptop computers with radio signal sending and receiving capabilities forming an ad-hoc network on the fly. However, most business networks use a wireless station connectivity enabling a mobile user with a laptop to set up a wireless connection to a hub. The laptop computers still have to be connected to an antenna for transmission to and from the hub. A portable radio antenna may be connected to the laptop through its PCMCIA (Personal Computer Memory Card International Association) slot. The hub that communicates via its own antenna is associated with a server for the client wireless computers.
The IEEE Industry Standard 802.11B Architecture (IEEE 802.11B) extensively used for wireless LAN transmissions in the frequency range of 2.4–2.4835 GHz of spread spectrum radio transmission.
A major problem with these spread spectrum wireless LAN transmissions is that they are not very secure. They are vulnerable to eavesdropping done with relatively simple radio equipment. Anyone equipped with a suitable transceiver within the range of transmission can eavesdrop. In a simple eavesdropping operation, any intruder may circle the perimeter of the target facility in a car or truck equipped with a transceiver and pick up messages since the 2.4 GHz signals must have a range extending for at least a short distance beyond the perimeter of the LAN area. Normally, this type of eavesdropping is not detectable since the sender or the intended receiver has no way of knowing whether the transmission has been intercepted.
A conventional way that users of wireless LANs have defended themselves against the eavesdropping intruders is through encryption of the transmissions with the LAN area. The wireless messages may be encrypted by the client computers in the LAN as well as by the LAN server, e.g. the LAN server associated with the hub. This has presented a problem to the eavesdropping intruders. However, the intruders have been attempting to decipher the encryption keys by a process that involves addressing a message to one of the client wireless client computers in the target LAN. The intruder then expects that the message will be encrypted through the LAN server so that it will be wirelessly transmitted to the addressee client computer in the LAN. The intruder then eavesdrops for the encrypted message which he sent. Now, the intruder has both the unencrypted and encrypted message and can break the secret encryption key. Then all encrypted wireless transmissions within the LAN may be eavesdropped and decrypted.